Subject: [mobile-ip] Deleting Correspondent node Binding while away from Home.

From: [email-masked]
Date: Mon, 23 Sep 2002 14:29:58 +0530

This is regarding, deletion of a Correspondent node Binding,
while away from Home. I need clarifications on this particular
scenario.

1. A mobile node MAY choose to keep its location private and
send a Binding Update to such a correspondent node to instruct
it, to delete any existing binding for the mobile node from its
Binding Cache, as described in Section 6.1.7.

   In section 6.1.7, it is mentioned that, the deletion of a
binding can be indicated by setting the Lifetime field to 0 or
by setting the care-of address equal to the home address.

Does it mean, for deletion (to keep its location private),
a mobile node can specify one of them?

If so, then why in Binding Refresh Request case, it is mentioned
that the mobile node SHOULD return a Binding Update to the sender,
in which the Lifetime field is set to zero and the care-of address
(using a Alternate Care-Of Address option) is set to the
mobile node's home address.

How this case of replying to BRR for deletion, is different
from the previous one?

In both the cases, it is MN which decides not to give Binding.
Then, why in replying to BRR we have to specify both.
How, it is different in this case?

2. For de-registration with a CN (while MN away from home) using
an alternate care-of address option (ACoA = Home address), should
MN need to send a Coti message as part of RR procedure?

If no, then should it use Home cookie as both Care-of Cookie
& Home cookie in calculation of Session key?

If so, then any node who has the home cookie can delete the
MN's Binding without the knowledge of the MN.
Ofcourse, I accept that the path between MN to HA is secure,
and HA to CN is not under MobileIPv6 scope.
So, are we assuming de-registration should be secure. Is this,
the intended idea or my assumptions are wrong?.

Thanks in advance
Srinivasan.D

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From: Jari Arkko <[email-masked]>
Date: Mon, 23 Sep 2002 16:30:48 +0300

> How, it is different in this case?

They aren't really different. 9.4.1 also contains the same
explanation as appears in 6.1.7. My suggestion is that we
change the BRR section as follows:

   Instead, if the mobile node chose to delete its binding from the
   sender of the Binding Refresh Request, the mobile node SHOULD return a
   Binding Update to the sender as follows. The Lifetime field is
   zero. The care-of address (using the Alternate Care-Of Address option)
   is the mobile node's home address.

=>

   Instead, if the mobile node chose to delete its binding from the
   sender of the Binding Refresh Request, the mobile node SHOULD return a
   Binding Update to the sender with the Lifetime specified as zero or
   specify a Care-of Address that matches the home address for the binding.

Let's make this issue #116.

(I'm not sure why the protocol originally allowed two ways to delete
bindings; does someone remember? We could require lifetimes to be non-zero
if a real care-of address is specified...)

> the intended idea or my assumptions are wrong?.

The current design is that home and care-of cookies are really
similar, just different addresses are used to create them (but #98
questions this a bit).

The current scheme allows you to use a home cookie twice when
you de-register, as you observed. I don't believe this is a
security threat, as anyone who is on the HA - CN could in
any case cause any kind of trouble, including dropping all
packets, modifying all packets, etc.

I'll mark this as issue #117 just in case we need to explain
the use-the-home-cookie-twice approach in the document. Currently
it isn't explained, as far as I remember.

Jari

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From: Jari Arkko <[email-masked]>
Date: Tue, 24 Sep 2002 15:57:53 +0300

responding my own mail from yesterday...

> it isn't explained, as far as I remember.

I have thought about this some more. I think we should be
satisfied with just making a HOTI-HOT exchange when returning
home, and not add a second exchange.

I also propose adding the following text to 11.5.1 after
the first paragraph:

   However, if the mobile node has a recently received home
   or care-of cookie and associated nonce indices for the desired
   addresses, it MAY reuse them. Note also that when returning home, the
   mobile node MAY use the home cookie and nonce index as a care-of
   cookie and nonce index.

Jari

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From: Vijay Devarapalli <[email-masked]>
Date: Tue, 24 Sep 2002 19:31:03 -0700

> by setting the care-of address equal to the home address.

for deregistering with the CN, the second option is never used.
the only way to send a deregister BU to the CN is by setting
the lifetime to 0. 

'setting the care-of address equal to the home address' is used
only when the MN returns home.

> a mobile node can specify one of them?

deregistering by way of setting the care-of address equal to
the home address is not related in any way to keeping the
MN's location private.

If the MN does not want the CN to know its current location,
it should not do Route Optimization. instead it should
reverse tunnel through its Home Agent.

Vijay